Frequency stabilization of magnetrons



April 10, 1951 w. M. PRESTON 2,548,816

FREQUENCY STABILIZATION OF MAGNETRONS Filed Sept. 19, 1945 MATCHING W RESISTOR -ao 25' moucnvs m DIAPHRAGM RESONANCE CAVITY FIG.|

- ANTENNA l2 MAJOR J WAVE GUIDE I MAGNETRON IN VEN TOR.

WILLIAM M. PRESTON BY ATTORNEY Patented Apr. 10, 1951 FREQUENCY STABILIZATION F .MAGNETRQNS William Preston, Lincoln,Mass., asslgnor, by

:mesneasfignmenta to the United States .91. America as represented by the Secretary of War Application September 19, 1945, Serial No. 617;3 17

1 Claim, 1

My invention relates in general to apparatus for'stabilizing electrical generatorsand more particularly to such apparatus which is associated Zvith high frequency electron oscillating appara- In the use of oscillators or generators employing thermionic tubes such for instance as the magnetron, it has .been found that the electrical properties thereof vary to a considerable degree and some means of stabilizing the frequency of the apparatus is necessary. Maintaining ade quate frequency stabilization is very difficult because the frequency of a magnetron -varies with the magnetic -field, radio frequency load, peak current and temperature. "This is in addition to the fact-that magnetrons are not identical when they are manufactured. These effects will cause an undesirable changein magnetron frequency and accordingly means must be developed to influence the frequency in such a fashion that it is comparatively stable. Accordingly, it is one of the objects of my invention to provide such an apparatus.

The stabilizing of the tube can be influenced by apparatus which controls or influences the tuning of the magnetron. Accordingly, it is another of the objects of my invention to provide anapparatus in which the tuning of the magnetron maybe influenced by apparatus external thereto.

In the stabilizing apparatus per se, it has been found necessary to decrease the danger of obtaining arcs of radio frequency energy resulting from the currentsinvolved in the apparatus passing into very high impedance such for instance as found when a resonantoavity type of stabilizer is used. Accordin ly, it is another of the objects of my invention to-provide an apparatus in which this danger may be minimized because for some frequencies it may be possibleto accomplish the result of this preceding paragraph by inserting a resistive load in series with the resonant cavity used. However, when ultra-high frequencies are used it has been found that special means must be provided for accomplishing this result. Heretofore dissipative loads such assand have .been used to some degree but'have not been found to be the answer to the problem when ultra-high frequenciesiare developedand utilized. Accordingly, it is another of the objects of my invention to provide such a load arrangement which may be used in conjunction with-the resonant cavity for use in a system such as described hereinafter.

In general, my apparatus contemplates the provision of a generator employing thermionic apparatus such for instance as a magnetrontype of tube. The magnetron maybe coupled to a main wave guide which is adapted to furnish energy to a radiating structure. Cut inthe main wave guide'is a slot or open section and a second or branch wave guide is provided which embraces the opening in the main guide and is adjustable relatively thereto. Connected to the branch guide is a resonant cavity whose parameters are adjustable. The output of the branch guide may be fed into a'lumped load or dummy load for schematically;

Fig. 2 isa showing of themain waveguide with a slot therein;

Fig. 3 is a perspective view of a-branch guide with its associated resonant cavity;

Fig. 4 shows a dummy load with its arrangedevice H for the purpose of passing energy to a main wave guide I2. The entire structure of the latter is not shownybut is merely'indicated-as feeding energy :to a radiating means identified bythe term antenna. The-main guidehas an open section orslot cut in one of the larger faces thereof and which will be more-clearly shown in Fig. 2. Embracing the main guide is an apparatus I-5 which is joined to a'minor or'branch guide Hi. The face of the guide l2 being slotted fora portion of its length, energy may be fed through the slot to the-branchguide Hi. The supporting member l5 has-joined thereto two spring members I! and I8 which'are adapted'topress against the-face of the main guide 'opposi-te'to-that' which is slotted for the purpose of having the branch guide pull firmlyvinto contact with the face 0 the'main guide containing the slot.

Associated "with the branch guide and fed thereby is a resonant cavity inclosed-by-the member 20 which has an opening thereof positioned adjacent an opening in the branch guide so as to be fed thereby. This is identified in the drawing by the terminology circular iris and the iris is positioned a distance from the main guide which is an odd multiple of a quarter Wavelength of the generated wave. Positioned within the branch guide and at a section thereof remote from the juncture from the main guide of the branch guide is an inductive diaphragm 25 and the end of the branch guide is terminated in a matching resistor 30.

Referring to Fig. 2, there is shown a perspective view of the main type of guide. This consists of substantially rectangular guide I2 having a slot 35 cut in one face thereof. of the guide terminat mechanical coupling members 36 and 31. Also joined to one of the faces is a member 38 having a threaded aperture which is adapted to be engaged by a screw member for moving the branch guide relatively to the main guide.

Referring to Fig.- 3, there is shown a perspective viewof a branch guide with its associated resonant cavity. The resonant cavity 60 is adapted to have its parameters changed by turning of th dial knob M. A scaled member 42 is positioned adjacent to dial knob for the purpose of indicating the parameters of the cavity at any one time. Mechanically joined to the cavity and adapted to feed the cavity is the minor or branch guide 16 one end of which has a mechanical coupling member 35 and the other end of which is fastened to member 8%. The member 46 is adapted to embrace at least a portion of the main guide at the position thereof where the slot 35 is located and hence energy will pass through the slot through the branch guide. For purposes of clarity, the end plate containing the spring members I! and It has been omitted from this drawing. Joined to the member 46 is a member 41 which is apertured and threaded and passing therethrough is a screw member 48 adapted to be turned by knob 49. The screw member engages the portion 38 of the main guide and turning of the knob Will produce relative movement between the main In practice the correct setting of the cavity mount can be found quickly by detuning the stabilizing cavity a considerable distance either above or below the magnetron frequency. The sliding section may be moved in smaller incremental steps and at each position thereof magnetron frequency may be measured. As the cavity is moved away from the magnetron the frequency will decrease continuously to a minimum value and then jump abruptly to a higher value and again decrease. The correct position is that at which the frequency jump occurs.

Since the operating frequency of the magnetron is pulled toward the resonant frequency of theresonant cavity the latter tends to stabilize the frequency to some extent. It is for this reason that the cavity assembly is called or may b referred to as a stabilizing tuner.

The ends The use of minor guides as stabilizing elements has been known heretofore to the art to which this case belongs and the use of the resonant cavity associated with the minor guides also is known to the art. With the arrangement according to this invention, however, the slide unit moving back and forth across the slot in the wave guide [2 easily allows the positioning of the minor guide so that the distance D is adjusted very easily and further the resistive load 38 provided at the end of the guide makes the adjustment of the distance D less critical. In addition the inductive diaphragm is placed at such a position in the minor or branch guide [6 so that it appears as a resistance at the resonant cavity iris and likewise at the entrance to the main guide provided the guide beyond the diaphragm is terminated in a matched load.

It will be appreciated that there may be deviations from the particular showing of this invention which will still remain within the spirit and scope thereof. Accordingly, I claim all such departures as fall fairly within the spirit and scope of the hereinafter appended claim.

What is claimed is:

A magnetron tuning system comprising a magnetron, a major wave-guide, means for coupling said magnetron to said major wave-guide, said major wave-guide having a first aperture, a slid ing sleeve fitting over said major wave-guide and said first aperture, a second aperture'in said sleeve of smaller dimensions than the dimensions of said first aperture, a minor wave-guide fixed by fitting into said second aperture and opening into said major wave-guide, a cavity res'- onator electrically coupled to said minor waveguide, an impedance matching device at the outer end of said miner wave-guide, said impedance matching device including a matching resistance connected to the end of said minor wave-guide and an inductive diaphragm positioned in said minor wave-guide near the end thereof so as to make said minor wave-guide appear as a resistance at the junction point of the major and minor wave-guides, a first means positioning said minor wave-guide substantially to a point on said major Wave-guide at which the magnetron frequency jumps, and a second means for altering the resonance frequency of said cavity, the relative positions of said first and second means adjusting the frequency of said magnetron.

WILLIAM M. PRESTON.

REFERENCES CITED The following references are of record in the file of this patent:

V UNITED STATES PATENTS Number 2,473,448 Rieke June 14, 1949 

